An inkjet recording apparatus is used as an image recording apparatus (or may be referred to as image forming apparatus) such as a printer, a facsimile or a copy machine. The inkjet recording apparatus records an image on a recording sheet or recording paper by ejecting droplets of ink toward the recording paper from an ink recording head. The recording sheet is not limited to a regular recording paper but includes an OHP film, etc., and means an object onto which droplets of ink or developer can be applied. Hereinafter various kinds of recording sheet may be simply referred to as a recording paper or a sheet. The recording sheet may also be referred to as a medium to be recorded or a recording medium. The inkjet recording apparatus is capable of recording a high definition image at high speed. Moreover, the inkjet recording apparatus can be operated at a low running cost, and has little noise. Additionally, the inkjet recording apparatus has an advantage in that a color image is easily recordable using multicolor ink.
There is known an inkjet head having a thermal actuator, a shape memory alloy actuator or an electrostatic actuator, as an energy generating means for discharging ink. The thermal actuator uses a phase change caused by film boiling of a liquid by an electrothermal conversion element such as a piezoelectric element. The shape memory alloy actuator uses a phase change of metal caused by a temperature change. The electrostatic actuator uses an electrostatic force to discharge ink.
In the meantime, in an inkjet recording method, since ink is applied onto a recording paper, the recording paper may expand due to a water component contained in the ink. Such a phenomenon is referred to as cockling. A recording paper may become wavy due to cockling, which results in a change in a positional relationship between a nozzle of a recording head and the surface of the recording paper being recorded at a position to a position. If the magnitude of cockling becomes large, the recording paper may be brought into contact with the nozzle of the recording head in the worst case. In such a case, a nozzle surface of the recording head may become dirty or the recording paper itself may become dirty, which causes deterioration in image quality. Moreover, a landing position of an ink droplet may be shifted due to influence of cockling, and image quality is deteriorated also in such as case.
In order to solve the above-mentioned problems, an inkjet recording apparatus performs recording while locating a recording paper on a platen provided with a recess for absorbing cockling of the recording paper. Such a platen is used together with a spur having protrusions on an outer periphery thereof. However, there is a problem in that scratches are formed on an image on the recording paper by such a spur.
In the conventional inkjet recording apparatus, recording papers are conveyed by rollers. That is, for example, two pairs of rollers are arranged with a printing area located therebetween, and one of the pairs is a combination of a spur and a roller. However, according to such as structure, an accurate paper feed can be guaranteed only when a recording paper is engaged with both the tow pairs of rollers.
In recent years, there is a demand for increasing a recordable area of a recording paper. Thus, there is an inkjet recording apparatus which records an image on a recording paper so as to acquire a large recordable area even when the recording paper is in engagement with only one of the pairs of rollers, that is, when the paper feed accuracy cannot be guaranteed. However, there may be a problem occurs when the recording paper is lifted in a stated where the recording paper is in engagement with only one of the two pairs of rollers. Additionally, the paper feed accuracy cannot be guaranteed since a sufficient paper feed force cannot be acquired, which results in a problem of deterioration in image quality.
In order to pursue an improvement in image quality in an inkjet recording apparatus, there is a demand for improving an accuracy of landing position of an ink droplet. Accordingly, it is necessary to improve a flatness of a recording paper to be recorded. However, as mentioned above, when recording is performed with a regular recording paper, fibers in the recording paper may be deformed in a wavy shape due to a water component contained in ink, which results in a displacement in a landing position of the ink droplet (dot). Thus far, it is found that such a deformation of a recording paper appears considerably large after more than three minutes have passed after ink droplets landed on the recording paper.
As disclosed in Japanese Patent Publication No. 2897960 and Japanese Laid-Open Patent Application No. 7-53081, in order to acquire flatness of a recording paper, there is suggested an inkjet recording apparatus that uses an endless charge belt which is electrically chargeable so as to electrostatically attract the recording paper onto the surface of the charge belt so that the recording paper is conveyed by rotationally moving the charge belt. Since the recording paper is prevented from being separated from the surface of the charge belt due to the electrostatic attraction force, high-flatness of the recording paper can be maintained by the charge belt while an inkjet recording operation is performed.
More specifically, Japanese Patent Publication No. 2897960 discloses a paper conveyance apparatus and an image recording apparatus that charges the surface of the charge belt in an alternating pattern by contacting a voltage applying means onto the surface of the charge belt. Japanese Laid-Open Patent Application No. 7-53081 discloses a printing apparatus that discharges the charge belt using a discharge belt so as to acquire a stable potential on the surface of the charge belt.
In the meantime, a material of the recording paper used in an image forming apparatus such as an inkjet recording apparatus is not limited to one kind since an OHP sheet, etc., may be used other than a regular recording paper.
In the case where a recording paper is conveyed by being electrostatically attached onto a conveyance belt (the same as the conventional charge belt), an electrostatic attraction force is changed since a rate of dielectric polarization changes due to an influence of electric charge on the conveyance belt caused by a surface resistivity of the recording paper to being conveyed.
Accordingly, in the conventional paper conveyance apparatus and image forming apparatus, when a kind of a recording paper used is changed, a desired electrostatic attraction force may not be acquired, which may prevents the recording paper from being conveyed in a stable condition. Thus, there is a problem in that deterioration occurs in a conveyance stability and image quality.